Internet protocol networks, often referred to as IP networks, are complex systems used by telecommunication service providers to provide high bandwidth transmission of data packets, often over long distances. Data transmitted over an IP network may be Internet related data, but may also be data for any other purpose, such as voice telephone calls transmitted using voice over IP protocols.
An IP network comprises a plurality of high bandwidth links, such as high capacity fiber optic cables or, more typically, a bundle of high capacity fiber optic cables, connecting telecommunication equipment, such as routers. Routers and other equipment may be co-located in points of presence, often referred to as PoPs. Packets of data are transmitted from a first router to a second router over the intermediate link connecting the first and second routers. To transmit a data packet from an origin router in an IP network to the destination router, the data packet is transmitted in a series of “hops” from one router to the next until it reaches its destination. The node at which a packet begins is referred to as the origin node, with the final node being referred to as the destination node. At each router on the path, that router independently determines the shortest path route to the destination and transmits the packet on the next hop of that shortest path route. A measure of the total traffic on any link of the IP network may be obtained by measuring packets transmitted or received by the routers connected by that link, as each link joins two, and only two, routers. Accordingly, the total amount of traffic on a link over a given time period may be determined based upon the traffic transmitted and/or received by the routers on either end of that link, over the link. A variety of methods are currently used to measure such link utilization values, and other methods may be developed in the future.
End-to-end packet delay, that is, the delay between the origin node and the destination node, is an important metric to measure in networks, both from the network operator and application performance points of view. An important component of this delay is the time it takes for packets to traverse the different forwarding elements along the path. This is particularly important for network providers who may have Service Level Agreements (SLAs) specifying allowable values of delay statistics across the domains they control. A fundamental building block of the path delay experienced by packets in IP networks is the delay incurred when passing through a single IP router.
Although there have been many studies examining delay statistics measured at the edges of the network, very few have been able to report with any degree of authority on what actually occurs at the switching elements. For instance, in one study, an analysis of single hop delay on an IP backbone network was presented and different delay components were isolated. See, Analysis of Measured Single-Hop Delay from an Operational Back Bone Network, K. Papagiannaki et al., Proc. IEEE Infocom, New York (2002). However, since the measurements in this study were limited to a subset of the router interfaces, only samples of the delays experienced by some packets on some links were identified. Single hop delays obtained for a router having only one input link and one output link, which links were of the same speed, have also been examined. However, this atypical operating scenario leads to the through-router delays being extremely low and not indicative of behavior in practical applications as the internal queueing with such an experimental setup is extremely limited.
Additionally, models have been proposed for inferring delays based solely on average link utilization. These methods, however, are fundamentally flawed as detailed statistics regarding the input traffic are not known. In fact, link utilization alone can be very misleading as a way of inferring packet delays. Suppose, for instance, that there is a group of back-to-back packets on a given output link of a store and forward-type router. That is, suppose that the packets follow each other on the link without gaps, i.e., the local link utilization is 100%. However, this does not imply that these packets have experienced large delays inside the router. They could very well be coming back-to-back from the input link with the same bandwidth as the output link. In this case, they would actually cross the router with minimum delay in the absence of cross-traffic.
To the inventors' knowledge, there have been no models constructed which provide for the measurement of delay within a router, referred to herein as “through-router delay”, with useful accuracy.
Thus, it would be advantageous to provide a comprehensive picture of end-to-end router delay performance without making any assumptions on traffic statistics or router functionalities. Further, it would be desirable to investigate how packet delays occur inside the router, that is, to provide a physical model of the router delay performance. Still further, it would be advantageous to summarize and report delay statistics effectively using existing protocols.